Universal driveshaft assembly

ABSTRACT

A driveshaft assembly includes a driveshaft including a longitudinal shaft axis, a first end, a second end, and a radially outer surface. The first end includes a plurality of recesses extending radially inward from the radially outer surface. The recesses each include a convex engagement surface. The driveshaft assembly also includes a first end housing including a longitudinal housing axis and an axially extending receptacle. The receptacle includes a plurality of planar receptacle surfaces. In addition, the driveshaft assembly includes a plurality of torque transfer keys configured to transfer torque between the driveshaft and first end housing. Each of the torque transfer keys includes a planar key surface and a concave key surface. The convex engagement surface of each recess engages the concave key surface of one of the torque transfer keys. The planar key surface of each torque transfer key engages one of the planar receptacle surfaces.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/325,475 filed Jan. 11, 2017 (now U.S. Pat. No. 10,408,274, which is a35 U.S.C. § 371 national stage entry of PCT/US2015/040513, filed Jul.15, 2015, and entitled “Universal Driveshaft Assembly,” which claims thebenefit of U.S. provisional patent application Ser. No. 62/025,322 filedJul. 16, 2014, and entitled “Universal Driveshaft Assembly,” and U.S.provisional patent application Ser. No. 62/025,326 filed Jul. 16, 2014,and entitled “Universal Driveshaft Assembly,” the contents of each ofthe foregoing are hereby incorporated herein by reference in theirentirety for all purposes.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

BACKGROUND

The disclosure relates generally to universal joints for transmittingtorque between rotating shafts having intersecting but non-coincidentrotational axes. More particularly, the disclosure relates to universaljoints for driveshafts employed in downhole motors used in the oil andgas drilling operations.

In drilling a borehole into an earthen formation, such as for therecovery of hydrocarbons or minerals from a subsurface formation, it isconventional practice to connect a drill bit onto the lower end of adrillstring formed from a plurality of pipe joints connected togetherend-to-end, and then rotate the drill string so that the drill bitprogresses downward into the earth to create a borehole along apredetermined trajectory. In addition to pipe joints, the drillstringtypically includes heavier tubular members known as drill collarspositioned between the pipe joints and the drill bit. The drill collarsincrease the vertical load applied to the drill bit to enhance itsoperational effectiveness. Other accessories commonly incorporated intodrill strings include stabilizers to assist in maintaining the desireddirection of the drilled borehole, and reamers to ensure that thedrilled borehole is maintained at a desired gauge (i.e., diameter). Invertical drilling operations, the drillstring and drill bit aretypically rotated from the surface with a top dive or rotary table.

During the drilling operations, drilling fluid or mud is pumped underpressure down the drill string, out the face of the drill bit into theborehole, and then up the annulus between the drill string and theborehole sidewall to the surface. The drilling fluid, which may bewater-based or oil-based, is typically viscous to enhance its ability tocarry borehole cuttings to the surface. The drilling fluid can performvarious other valuable functions, including enhancement of drill bitperformance (e.g., by ejection of fluid under pressure through ports inthe drill bit, creating mud jets that blast into and weaken theunderlying formation in advance of the drill bit), drill bit cooling,and formation of a protective cake on the borehole wall (to stabilizeand seal the borehole wall).

It has become increasingly common and desirable in the oil and gasindustry to drill horizontal and other non-vertical boreholes (i.e.,“directional drilling”), to facilitate more efficient access to andproduction from larger regions of subsurface hydrocarbon-bearingformations than would be possible using only vertical boreholes. Indirectional drilling, specialized drill string components and “bottomhole assemblies” are used to induce, monitor, and control deviations inthe path of the drill bit, so as to produce a borehole of desirednon-vertical configuration.

Directional drilling is typically carried out using a downhole or mudmotor incorporated into the bottom hole assembly (BHA) immediately abovethe drill bit. A typical downhole motor includes several primarycomponents, such as, for example (in order, starting from the top of themotor assembly): (1) a top sub adapted to facilitate connection to thelower end of a drill string (“sub” being the common general term in theoil and gas industry for any small or secondary drill string component);(2) a power section; (3) a drive shaft enclosed within a drive shafthousing, with the upper end of the drive shaft being coupled to thelower end of the rotor of the power section; and (4) a bearing assembly(which includes a mandrel with an upper end coupled to the lower end ofthe drive shaft, plus a lower end adapted to receive a drill bit). Thepower section is typically a progressive cavity or positive displacementmotor (PD motor). In a PD motor, the rotor comprises a shaft formed withone or more helical vanes or lobes extending along its length, and thestator is formed of an elastomer liner bonded to the inner cylindricalwall of the stator housing. The liner defines helical lobescomplementary to that of the rotor lobe or lobes, but numbering one morethan the number of rotor lobes. The lower end of the rotor comprises anoutput shaft, which in turn is coupled to the upper end of a drive shaftthat drives the rotation of the drill bit.

In drilling operations employing a downhole motor, drilling fluid iscirculated under pressure through the drill string and back up to thesurface as previously described. However, in route to the drill bit, thepressurized drilling fluid flows through the power section of thedownhole motor to generate rotational torque to rotate the drill bit. Inparticular, high-pressure drilling fluid is forced through the powersection, causing the rotor to rotate within the stator, and inducing apressure drop across the power section (i.e., the drilling fluidpressure being lower at the bottom of the power section). The powerdelivered to the output shaft is proportional to the product of thevolume of fluid passing through the power section multiplied by thepressure drop across the power section (i.e., from fluid inlet to fluidoutlet). Accordingly, a higher rate of fluid circulation fluid throughthe power section results in a higher rotational speed of the rotorwithin the stator, and correspondingly higher power output.

As previously noted, the output shaft is coupled to the upper end of thedrive shaft, for transmission of rotational torque to the drill bit.However, the motion of the rotor in a PD motor is eccentric in nature,or “precessional”—i.e., in operation, the lower end of the rotor (i.e.,the output end) rotates or orbits about the central longitudinal axis ofthe stator housing. The output shaft is coupled to the upper end of thedrive shaft with a first (or upper) universal joint, thereby allowingrotational torque to be transferred from the rotor to the drive shaftirrespective of the eccentric motion of the rotor or fact that theoutput shaft and drive shaft are not coaxially aligned.

The bearing assembly typically incorporates an elongate tubular mandrelhaving an upper end coupled to the lower end of the drive shaft by meansof a second (or lower) universal joint, and a lower end coupled to thedrill bit. The mandrel is encased in a tubular bearing housing thatconnects to the tubular drive shaft housing above. The mandrel rotatesconcentrically within the bearing housing.

The universal joint assemblies of conventional driveshafts are prone tosubstantial wear and may fail relatively quickly during operation. Inparticular, many such conventional driveshafts transfer torque througheither point or line contact(s), which disperse a large amount of forceover a relatively small surface area, thereby tending to accelerate wearat such contact surfaces.

BRIEF SUMMARY OF THE DISCLOSURE

Some embodiments disclosed herein are directed to a driveshaft assembly.In an embodiment, the driveshaft assembly includes a driveshaftincluding a longitudinal shaft axis, a first end, a second end oppositethe first end, and a radially outer surface. The first end includes aplurality of recesses extending radially inward from the radially outersurface, the recesses each comprising a planar engagement surface. Inaddition, the driveshaft assembly includes a first end housing includinga longitudinal housing axis, and an axially extending receptacle. Thereceptacle includes a plurality of planar receptacle surfaces. Further,the driveshaft assembly includes a torque transfer assembly configuredto transfer torque between the driveshaft and the first end housing. Thetorque transfer assembly includes a plurality of torque transfer keyseach including a planar key surface and a convex key surface, and anadapter including a plurality of concave adapter surfaces and aplurality of planar adapter surfaces. The planar engagement surface ofthe each recess engages the planar key surface of one of the torquetransfer keys. In addition, the convex key surface of each torquetransfer key engages one of the concave adapter surfaces of the adapter.Further, each of the planar adapter surfaces of the adapter engage withone of the planar receptacle surfaces.

Other embodiments are directed to a driveshaft assembly. In anembodiment, the driveshaft assembly includes a driveshaft including alongitudinal shaft axis, a first end, a second end opposite the firstend, and a radially outer surface. The first end includes a plurality ofrecesses extending radially inward from the radially outer surface, therecesses each comprising a convex engagement surface. In addition, thedriveshaft assembly includes a first end housing including alongitudinal housing axis, and an axially extending receptacle. Thereceptacle includes a plurality of planar receptacle surfaces. Further,the driveshaft assembly includes a plurality of torque transfer keysconfigured to transfer torque between the driveshaft and first endhousing, each of the torque transfer keys including a planar key surfaceand a concave key surface. The convex engagement surface of each recessengages the concave key surface of one of the torque transfer keys, andthe planar key surface of each torque transfer key engages one of theplanar receptacle surfaces.

Embodiments described herein comprise a combination of features andcharacteristics intended to address various shortcomings associated withcertain prior devices, systems, and methods. The foregoing has outlinedrather broadly certain of those features and characteristics of thedisclosed embodiments in order that the detailed description thatfollows may be better understood. The various characteristics andfeatures described above, as well as others, will be readily understoodby those skilled in the art upon reading the following detaileddescription, and by referring to the accompanying drawings. It should beappreciated that the conception and the specific embodiments disclosedmay be readily utilized as a basis for modifying or designing otherstructures for carrying out the same purposes as the disclosedembodiments. It should also be realized that such equivalentconstructions do not depart from the spirit and scope of the teachingsdisclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of various embodiments, reference will now bemade to the accompanying drawings in which:

FIG. 1 is a schematic partial cross-sectional view of a drilling systemincluding an exemplary embodiment of a driveshaft assembly in accordancewith at least some embodiments;

FIG. 2 is a partial cross-sectional side view of the driveshaft assemblyof FIG. 1;

FIG. 3 is an enlarged cross-sectional side view of one of the universaljoint assemblies of the driveshaft assembly of FIG. 1;

FIG. 4 is a perspective view of the lower end of the driveshaft of FIG.1;

FIG. 5 is a front or axial view of the lower end of driveshaft of FIG.1;

FIG. 6 is another perspective view of the lower end of the driveshaft ofFIG. 1 illustrating the installation of a torque transfer assemblythereon in accordance with at least some embodiments;

FIG. 7 is a perspective view of one of the torque transfer keys of thetorque transfer assembly of FIG. 6;

FIG. 8 is a top view of one of the torque transfer keys of the torquetransfer assembly of FIG. 6;

FIG. 9 is a perspective view of the adapter of the torque transferassembly of FIG. 6;

FIG. 10 is a top view of the adapter of the torque transfer assembly ofFIG. 6;

FIG. 11 is an enlarged perspective view of one of the arms of theadapter of the torque transfer assembly of FIG. 6;

FIG. 12 is an enlarged top view of one of the arms of the adapter of thetorque transfer assembly of FIG. 6 illustrating the installation of oneof the torque transfer keys of FIG. 6 thereon;

FIG. 13 is a perspective view of the end housing of the universal jointassembly of FIG. 3;

FIG. 14 is a front or axial view of the end housing of the universaljoint assembly of FIG. 3;

FIG. 15 is a cross-sectional view of the universal joint assembly takenalong section XV-XV of FIG. 3;

FIG. 16 is a partial cross-sectional side view of another driveshaftassembly for use within the drill system of FIG. 1;

FIG. 17 is an enlarged cross-sectional side view of another universaljoint assembly for use in the driveshaft assembly of FIG. 1 inaccordance with at least some embodiments;

FIG. 18 is a perspective view of a lower end of the driveshaft of FIG.16;

FIG. 19 is a front or axial view of the lower end of driveshaft of FIG.16;

FIG. 20 is another perspective view of the lower end of the driveshaftof FIG. 16 illustrating the installation of torque transfer keys thereonin accordance with the at least some embodiments;

FIG. 21 is a perspective view of one of the torque transfer keys of FIG.20;

FIG. 22 is a top view of one of the torque transfer keys of FIG. 20;

FIG. 23 is a front view of one of the torque transfer keys of FIG. 20;

FIG. 24 is a perspective view of the end housing of the universal jointassembly of FIG. 17;

FIG. 25 is a front or axial view of the end housing of the universaljoint assembly of FIG. 17; and

FIG. 26 is a cross-sectional view of the universal joint assembly takenalong section XXVI-XXVI in FIG. 17.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The following discussion is directed to various exemplary embodiments.However, one of ordinary skill in the art will understand that theexamples disclosed herein have broad application, and that thediscussion of any exemplary embodiment is meant only to be illustrativeof that embodiment, and not intended to suggest that the scope of thedisclosure, including the claims, is limited to that embodiment.

The drawing figures are not necessarily to scale. Certain features andcomponents herein may be shown exaggerated in scale or in somewhatschematic form and some details of conventional elements may not beshown in interest of clarity and conciseness.

In the following discussion and in the claims, the terms “including” and“comprising” are used in an open-ended fashion, and thus should beinterpreted to mean “including, but not limited to . . . .” Also, theterm “couple” or “couples” is intended to mean either an indirect ordirect connection. Thus, if a first device couples to a second device,that connection may be through a direct connection, or through anindirect connection that is established via other devices, components,and connections. In addition, as used herein, the terms “axial” and“axially” generally mean along or parallel to a central axis (e.g.,central axis of a body or a port), while the terms “radial” and“radially” generally mean perpendicular to the central axis. Forinstance, an axial distance refers to a distance measured along orparallel to the central axis, and a radial distance means a distancemeasured perpendicular to the central axis. Any reference to up or downin the description and the claims is made for purposes of clarity, with“up”, “upper”, “upwardly”, “uphole”, or “upstream” meaning toward thesurface of the borehole and with “down”, “lower”, “downwardly”,“downhole”, or “downstream” meaning toward the terminal end of theborehole, regardless of the borehole orientation.

Referring now to FIG. 1, a system 10 for drilling a borehole 16 in anearthen formation is shown. In this embodiment, system 10 includes adrilling rig 20 disposed at the surface, a drill string 21 extendingfrom rig 20 into borehole 16, a downhole motor 30, and a drill bit 90.Motor 30 forms a part of the bottomhole assembly (“BHA”) and is disposedbetween the lower end of the drill string 21 and drill bit 90. Movingdownward along the BHA towards bit 90, motor 30 includes a hydraulicdrive or power section 40, a driveshaft assembly 100 coupled to powersection 40, and a bearing assembly 80 coupled to driveshaft assembly100. Bit 90 is coupled to the lower end of bearing assembly 80.

The hydraulic drive section 40 converts pressure exerted by drillingfluid pumped down drill string 21 into rotational torque that istransferred through driveshaft assembly 100 and bearing assembly 80 todrill bit 90. With force or weight applied to the drill bit 90, alsoreferred to as weight-on-bit (“\NOB”), the rotating drill bit 90 engagesthe earthen formation and proceeds to form borehole 16 along apredetermined path toward a target zone. The drilling fluid or mudpumped down the drill string 21 and through motor 30 passes out of theface of drill bit 90 and back up the annulus 18 formed between drillstring 21 and the sidewall 19 of borehole 16. The drilling fluid coolsthe bit 90, flushes the cuttings away from the face of bit 90, andcarries the cuttings to the surface.

Referring now to FIG. 2, driveshaft assembly 100 includes an outerdriveshaft housing 110, a driveshaft 120 rotatably disposed withinhousing 110, a first or upper end housing 130 coupled to driveshaft 120,and a second or lower end housing 140 also coupled to driveshaft 120.Housing 110 is an elongate, cylindrical tubular member having a centralor longitudinal axis 115, a first or upper end 110 a, and a second orlower end 110 b opposite upper end 110 a. As is best shown in FIG. 1, inthis embodiment, housing 110 is coaxially aligned with hydraulic drivesection 40 and bearing assembly 80. In addition, upper end 110 a ofhousing 110 is coupled to an outer housing of drive section 40 and lowerend 110 b of housing 110 is coupled to an outer housing of bearingassembly 80.

Referring still to FIG. 2, driveshaft 120 has a central or longitudinalaxis 125, a first or upper end 120 a, a second or lower end 120 bopposite end 120 a, and a generally cylindrical radially outer surface120 c extending axially between ends 120 a, 120 b. As will be describedin more detail below, axis 125 of shaft 120 is not coaxially alignedwith axis 115 of housing 110. An annular space 116 is formed betweendrive shaft housing 110 and driveshaft 120. During drilling operations,drilling fluid is pumped down drill string 21 and through downhole motor30 to drill bit 90. Within driveshaft assembly 100, drilling fluid flowsthrough annular space 116 from upper end 110 a to lower end 110 b inroute to bearing assembly 80 and drill bit 90.

Upper end housing 130 has a first or upper end 130 a, a second or lowerend 130 b opposite end 130 a, a connector section 132 extending fromupper end 130 a, and a socket section 134 extending from connectorsection 132 to lower end 130 b. In this embodiment, connector section132 is a male pin or ping end connector that threadably connects upperend housing 130 to the output shaft of hydraulic drive section 40.Socket section 134 receives upper end 120 a of drive shaft 120. As willbe described in more detail below, the coupling between upper end 120 aand socket section 134 allows driveshaft 120 to pivot about end 120 arelative to end housing 130 while simultaneously transferring rotationaltorque and axial thrust loads between end housing 130 and driveshaft120.

Lower end housing 140 has a first or upper end 140 a, a second or lowerend 140 b, a connector section 142 extending from upper end 140 a, and asocket section 144 extending from connector section 142 to the lower end140 b. In this embodiment, connector section 142 is a female box orbox-end connector that threadably connects lower end housing 140 to themandrel of bearing assembly 80. Socket section 144 receives lower end120 b of driveshaft 120. As will be described in more detail below, thecoupling between lower end 120 b and socket section 144 allowsdriveshaft 120 to pivot about end 120 b relative to end housing 140while simultaneously transferring rotational torque and axial thrustloads between end housing 140 and driveshaft 120.

In this embodiment, ends 120 a, 120 b of driveshaft 120 are structurallyidentical, and socket sections 134, 144 are structurally identical.Therefore, in the description to follow and associated Figures, thedetails of embodiments of the lower end 120 b, corresponding socketsection 144, and the coupling or connection therebetween are shown anddescribed, it being understood that embodiments of upper end 120 a,corresponding socket section 134, and the connection therebetween,respectively, may be the same.

Referring now to FIG. 3, an embodiment of lower end 120 b of driveshaft120 and socket section 144 of lower end housing 140 are shown. Socketsection 144 has a central or longitudinal axis 145 and includes areceptacle 146 that extends axially from end 140 a and receives lowerend 120 b of driveshaft 120. It should be noted that, while axes 125,145 are shown generally aligned in FIG. 3, the axis 125 of driveshaft120 is typically misaligned with axis 145 of socket section 144 due tothe pivoting of driveshaft 120 about end 120 b during operations.

Referring briefly to FIGS. 3, 13, and 14, receptacle 146 is defined by aradially inner surface 146 c. Moving axially from upper end 140 a, innersurface 146 c includes an upper generally cylindrical surface 308extending axially from upper end 140 a, a plurality of circumferentiallyspaced shoulders 306 extending radially inward from surface 308 (e.g.,in this embodiment, there are a total of four shoulders 306), aplurality of circumferentially spaced pockets 302 extending axially fromshoulders 306, a generally planar surface 304 extending radially frompockets 302, and a cylindrical counterbore or recess 320 extendingaxially from surface 304. Shoulders 306 and surfaces 304 are planarsurfaces disposed in planes oriented perpendicular to axis 145. Inaddition, in this embodiment, receptacle 146 includes a total of fourpockets 302 spaced uniformly circumferentially about axis 145, such thateach pocket 302 is disposed approximately 90° from eachcircumferentially adjacent pocket 302.

Referring back now to FIG. 3, in this embodiment, a bearing insert 180is disposed within recess 320. Insert 180 includes a body 181 coaxiallyaligned with the axis 145 and having a first or upper end 181 a, and asecond or lower end 181 b opposite the upper end 181 a. In thisembodiment, the upper end 181 a includes a generally upward facingconcave spherical bearing surface 182, and lower end 181 b comprises agenerally planar surface 186 oriented perpendicular to axis 145. Asshown in FIG. 3, planar surface 186 of insert 180 is seated withinrecess 320 such that bearing surface 182 faces axially upward. As isshown in FIG. 3 lower end 120 b of shaft 120 includes a cavity 121extending axially inward from lower end 120 b and having a concavespherical ball seat or surface 123 that receives a thrust sphere or ball122. When lower end 120 b is mounted within receptacle 146, upper end181 a of body 181 extends into cavity 121 such that concave sphericalbearing surface 182 mates with and slidingly engages ball 122.

Referring still to FIG. 3, a mounting collar 148 is disposed within thereceptacle 146 proximate upper end 140 a. In general mounting collarincludes a radially outer surface 148 a, and a radially inner surface148 b. Collar 148 is threaded into receptacle 146, via engagement ofmating external threads on outer surface 148 a and internal threads onsurface 308. An annular seal assembly 150 is radially positioned betweensurfaces 148 a, 308 to prevent fluid flow therebetween.

A flexible closure boot 164 is provided to prevent drilling mud fromflowing into receptacle 146 during drilling operations. Closure boot 164is disposed about driveshaft 120 proximate lower end 120 b and has afirst or upper end 164 a coupled to driveshaft 120 with a lock ring 160and a second or lower end 164 b coupled to end housing 140 with collar148 and an L-shaped compression ring 166. Thus, closure boot 164 extendsradially between driveshaft 120 and end housing 140. More specifically,upper end 164 a of boot 164 is seated in an annular recess on outersurface 120 c of driveshaft 120, and a lock ring 160 is disposed onshaft 120 over end 164 a, thereby holding end 164 a in position betweenring 160 and shaft 120 via an interference fit. A snap ring 162 isdisposed in a circumferential groove 163 in outer surface 120 c andaxially retains ring 160 on shaft 120. Lower end 164 b of boot 164 issimilarly held in position through an interference fit. In particular,lower end 164 b is seated on radially inner surface 148 b and compressedbetween collar 148 and compression ring 166 disposed in receptacle 146.

Referring now to FIGS. 3-5, lower end 120 b of driveshaft 120 is shown.In addition to cavity 121 previously described, lower end 120 b includesa plurality of recesses 124 extending both radially inward from outersurface 120 c and axially from lower end 120 b. Each recess 124 is atleast partially defined by a first planar surface 126, and a secondplanar surface 128. In this embodiment, the surfaces 126, 128 of eachrecess 124 are each perpendicular to one another such that each recess124 is substantially V-shaped when viewed in cross-section along axis125 (e.g., as shown in FIG. 5). As will be described in more detailbelow, during drilling operations, torque is transferred from driveshaft120 through the surface 126 of each recess 124, and thus, first planarsurface 126 of each recess 124 may be referred to herein as anengagement or torque transfer surface 126.

In this embodiment, lower end 120 b includes a total of four recesses124 uniformly circumferentially disposed about axis 125 such that eachrecess 124 is disposed approximately 90° from each circumferentiallyadjacent recess 124. As a result, the planar surfaces 126, 128 of eachrecess 124 are generally parallel to the planar surface 126, 128,respectively, of each radially opposing recess 124 (i.e., the recess 124disposed 180° from the recess 124 in question) with respect to axis 125.Moreover, in this embodiment, each of the surfaces 126, 128 are parallelto the central axis 125 of driveshaft 120; however, in otherembodiments, surfaces 126, 128 are not parallel to axis 125 and areinstead disposed at some non-zero angle thereto.

As will be described in more detail below, during rotation of shaft 120about axis 125, shaft 120 is free to pivot at lower end 120 b about afirst pivot axis 127 and a second pivot axis 129. Axes 127, 129 areoriented orthogonal to each other and intersect at a center point 119disposed along axis 125. Thus, axes 125, 127, 129 all intersect atcenter 119. In addition, axes 127, 129 lie in a plane orientedperpendicular or orthogonal to axis 125. Further, in this embodimentcenter 119 also corresponds to the center of curvature of concavespherical surface 123 in cavity and the center of thrust ball 122 whenball 122 is installed within cavity 121 as previously described (e.g.,see FIG. 3). Thus, sliding engagement between thrust ball 122 andsurface 123 of cavity 121 and sliding engagement between ball 122 andsurface 182 of bearing insert 180 allows driveshaft 120 to pivot aboutcenter 119 during operations.

Referring now to FIGS. 3 and 6, a torque transfer assembly 185 isdisposed about lower end 120 b of driveshaft 120 within receptacle 146and transmits torque loads between driveshaft 120 and end housing 140 asdriveshaft 120 rotates about axis 125. In this embodiment, torquetransfer assembly 185 generally includes a plurality of torque transferkeys 190 and an adapter 200. As will be described in more detail below,sliding engagement of the various surfaces of torque transfer assembly185 (i.e., mating surfaces of keys 190 and adapter 200) allow driveshaft120 to transfer torque to end housing 140 through direct, face-to-faceengagement even as driveshaft 120 pivots about axes 127, 129 relative toend housing 140 as previously described.

Referring now to FIGS. 7 and 8, each of the torque transfer keys 190 isgenerally D-shaped and is disposed on adapter 200. As is best shown inFIG. 7, each key 190 comprises a body 192 having a central axis 195, afirst or top side 192 a, a second or bottom side 192 b axially oppositethe top side 192 a, a first lateral side 192 c, and a second lateralside 192 d radially opposite the first lateral side 192 c. In thisembodiment, the axis 195 passes through the center of mass of key 190and is parallel to one of the axes 127, 129 when driveshaft assembly 100is fully made up. In addition, in this embodiment, sides 192 a, 192 bcomprise parallel planar surfaces 193, 199, respectively, orientedperpendicular to axis 195; side 192 c comprises a planar torque transfersurface 194 extending axially between sides 192 a, 192 b; and side 192 dcomprises a convex cylindrical surface 196 extending axially betweensides 192 a, 192 b. Surface 196 is concentric about an axis of curvature197 that is oriented parallel to axis 195 and surface 194, and radiallyspaced from axis 195 and surface 194. Axes 195, 197 lie in a planeoriented perpendicular to surface 194. Further, in this embodimentsurfaces 194, 196 each intersect chamfered surfaces 198 a, 198 b, suchthat surface 194 has a length L₁₉₄ extending between surfaces 198 a, 198b; however, it should be appreciated that other embodiments of keys 190may not include chamfered surfaces 198 a, 198 b. Still further, surface196 has a radius R₁₉₆ measured radially from axis of curvature 197 tosurface 196. Moreover, as will be described in more detail below, inthis embodiment, axis 197 of each key 190 is aligned with one of thepivot axes 127, 129 when assembly 100 is fully made up.

Referring now to FIGS. 9-11, adapter 200 includes a central orlongitudinal axis 205 that is aligned with axis 145 of end housing 140when adapter 200 is installed within receptacle 146 (e.g., as shown inFIG. 3), a plurality of engagement arms 202, and a central connectingmember 204. Connecting member 204 is formed of a single plate thatincludes a first or upper side 204 a and a second or lower side 204 bopposite upper side 204 a, where sides 204 a, 204 b are parallel to oneanother and are each perpendicular to axis 205. In addition, member 204is shaped to correspond with receptacle 146. Namely, in this embodiment,connecting member 204 includes a plurality of radial extensions 203 thatgenerally correspond in shape and arrangement with pockets 302 ofreceptacle 146 previously described such that each extension 203 fitswithin one of the pockets 302 of receptacle 146 when adapter 200 isfully installed therein. Thus, in this embodiment adapter 200 includes atotal of four extensions 203 that are uniformly circumferentially spacedabout axis 205 such that each extension 203 is disposed approximately90° from each circumferentially adjacent extension 203. In addition, onearm 202 extends axially outward from upper side 204 a on each of theextensions 203, such that in this embodiment, there are a total of fourarms 202 uniformly circumferentially spaced about axis 205 and each arm202 is disposed approximately 90° from each circumferentially adjacentarm 202. In addition, a hole or aperture 206 extends axially throughmember 204, between sides 204 a, 204 b and is coaxially aligned withaxis 205. As will be described in more detail below, hole 206 is sizedto allow passage of upper end 181 a of body 181 of bearing insert 180therethrough during operations.

As is best shown in FIG. 11, each arm 202 includes central axis 215 thatis parallel to and radially spaced from axis 205 of adapter 200, a firstend 202 a, and a second end 202 b opposite first end 202 a. In addition,each arm 202 includes a first driveshaft facing side 202 c, a first endhousing facing side 202 d radially opposite first driveshaft facing side202 c with respect to axis 215, a second driveshaft facing side 202 eextending between sides 202 c, 202 d, and a second end housing facingside 202 f also extending between sides 202 c, 202 d and radiallyopposite second driveshaft facing side 202 e with respect to axis 215.Each side 202 c, 202 d, 202 e, 202 f extends axially between ends 202 a,202 b. First end housing facing side 202 d includes an axially extendingplanar engagement surface 209, while a cylindrical recess 208 extendsradially inward from side 202 c with respect to axis 215. Recess 208 isdefined by a concave cylindrical surface 212 having an axis of curvature213 and a planar floor surface 210 extending between side 202 c andconcave cylindrical surface 212.

Referring now to FIGS. 6 and 12, during make up of torque transferassembly 185, each of the keys 190 are disposed within one of therecesses 208 on arms 202 of adapter 200. In particular, each key 190 isdisposed within one of the recesses 208 such that one of the parallelplanar surfaces 193, 199 slidingly engages floor surface 210, and convexcylindrical surface 196 slidingly engages concave cylindrical surface212. In addition, as is best shown in FIG. 12, when keys 190 aredisposed within recesses 208 as described above, the axis of curvature197 of each surface 196 on each key 190 aligns with and is thereforecoincident with the axis of curvature 213 of the respective,corresponding surface 212 in recess 208. Thus, during operations, eachkey 190 is allowed to pivot or rotate about the aligned axes 197, 213through sliding engagement of the surfaces 196, 212 and slidingengagement of one of the surfaces 193, 199 and the surface 210. Inaddition, as will be described in more detail below, in this embodimentwhen assembly 185 is fully installed on lower end 120 b of driveshaft120 and lower end 120 b and assembly 185 are both fully inserted withinreceptacle 146 of end housing 140 (e.g., FIG. 3), the aligned axes 197,213 of each of the arm 202 and key 190 pairs are further aligned withone of the pivot axes 127, 129, previously described, such that duringoperation, each of the keys 190 pivot or rotate about one of the pivotaxes 127, 129 to further facilitate pivoting of driveshaft 120 aboutaxes 127, 129 relative to end housing 140.

Referring again to FIGS. 13 and 14, in this embodiment each pocket 302of receptacle 146 is defined by a first planar surface 310, a secondplanar surface 312 parallel to the first planar surface 310, a thirdplanar surface 314 extending perpendicularly or orthogonal from thefirst planar surface 310, and a fourth planar surface 316 extendingbetween surfaces 312, 314. In this embodiment, each of the surfaces 310,312, 314, 316 extend axially or parallel to axis 145 of end housing 140;however, such an arrangement is not required such that in otherembodiments, surfaces 310, 312, 314, 316 are disposed at some non-zeroangle to axis 145. As will be described in more detail below, each ofthe first planar surfaces 310 of pockets 302 engage with mating surfacesin torque transfer assembly 185 (e.g., planar surfaces 209 on arms 202)in order to transfer torque between shaft 120 and end housing 140 duringrotation of driveshaft 120 about axis 125. Thus, surfaces 310 may bereferred to herein as either engagement or torque transfer surfaces.

As is also best shown in FIG. 14, pockets 302 are arranged withinreceptacle 146 such that the first planar engagement surface 310 of eachpocket 302 extends to the second planar surface 312 of the immediatelycircumferentially adjacent pocket 302. In addition, the first planarengagement surfaces 310 of radially opposing pockets 302 (i.e., pockets302 that are circumferentially disposed 180° from one another about axis145) are generally parallel to one another. Such a parallel relationshipof surfaces 310 ensures that torque transfer between driveshaft 120 andend housing 140 is more evenly distributed.

Referring now to FIGS. 3, 6, and 15, the assembly of lower end 120 b ofdriveshaft 120, torque transfer assembly 185, and end housing 140 willnow be described. First, as is best shown in FIG. 6, torque transferassembly 185 is made up as previously described above and installed onlower end 120 b of driveshaft 120 such that each mating pair of keys 190and arms 202 is disposed within one of the recesses 124 on lower end 120b. In particular, keys 190 and adapter 200 are installed on lower end120 b of driveshaft 120 such that planar surfaces 194 engage with planarsurfaces 126 and second driveshaft facing sides 202 e of each arms 202oppose planar surfaces 128 within recesses 124. In addition, whenadapter 200 is fully installed on lower end 120 b, hole 206 is generallyaligned with cavity 121. Further, as is shown in FIG. 6, when torquetransfer assembly 185 is installed on lower end 120 b in thisembodiment, the aligned axes 197, 213 of surfaces 196, 212, respectivelyare further aligned with one of the pivot axes 127, 129. As will bedescribed in more detail below, such alignment with axes 197, 213, 127,129 allows keys 190 to pivot about one of the axes 127, 129 to furtherfacilitate pivoting of driveshaft 120 about axes 127, 129 duringdrilling operations. In this embodiment, either prior or subsequent toinstallation of torque transfer assembly 185 on lower end 120 b, thrustball 122 is installed within cavity 121 and is seated on concavespherical bearing surface 123 (e.g., see FIG. 3).

As is best shown in FIGS. 3 and 15, lower end 120 b of driveshaft 120,with torque transfer assembly 185 installed thereon, is then insertedwithin receptacle 146 on end housing 140 such that lower side 204 babuts or engages with planar surface 304, and upper end 181 a of body181 of bearing insert 180 extends through hole 206 and cavity 121 suchthat concave spherical bearing surface 182 on upper end 181 a engagesthrust ball 122. Therefore, thrust ball 122 is disposed between andengaged with concave spherical bearing surfaces 123, 182 as shown inFIG. 3. In addition, as lower end 120 b of driveshaft 120 and torquetransfer assembly 185 are installed within receptacle 146, each of thesurfaces 209 of first end housing facing sides 202 d on arms 202 engageswith one of the engagement surfaces 310 of pockets 302 as shown in FIG.15.

Referring still to FIGS. 3 and 15, once driveshaft assembly 100 is fullymade up, driveshaft 120 is free to pivot relative to lower end housing140 about center 119, while rotating about axis 125 in direction 113. Inparticular, as shaft 120 rotates about axis 125 in direction 113, end120 b of shaft 120 can pivot about one or both of the axes 127, 129through sliding engagement of thrust ball 122 on surface 123 withincavity 121 and concave spherical bearing surface 182 of insert 180.Additionally, pivoting of end 120 b of driveshaft 120 about axes 127,129 is further accommodated by sliding engagement of cylindrical surface196 of each key 190 and cylindrical surface 212 within recesses 208 onarms 202 of adapter 200 as well as sliding engagement of surfaces 194 oneach key 190 and planar surfaces 126 on lower end 120 b of driveshaft120.

Moreover, during rotation of shaft 120 about axis 125 in direction 113,torque is transferred between lower end 120 b and end housing 140through torque transfer assembly 185. In particular, torque is firsttransferred between lower end 120 b and keys 190 through engagement ofsurfaces 126, 194. Thereafter, torque is transferred between keys 190and adapter 200 through engagement of surfaces 196, 212. Finally, torqueis transferred between adapter 200 and end housing 140 throughengagement of surfaces 209, 310. Because keys 190 are allowed to pivotabout one of the axes 127, 129 within recesses 208 on arms 202 ofadapter 200 in this embodiment as previously described, keys 190 areable to maintain face-to-face contact between surfaces 194, 126 asdriveshaft 120 pivots about axes 127, 129 simultaneous with rotationabout axis 125 in direction 113. In this embodiment, the couplingbetween upper end housing 130 and upper end 120 a of driveshaft 120 isstructurally and functionally the same as the coupling between lower endhousing 140 and lower end 120 b of driveshaft described above; however,it should be appreciated that such structural symmetry is not required.In addition, while a specific order of assembly has been described abovefor lower end 120 b of driveshaft 120, it should be appreciated that thespecific assembly order may be greatly varied. For example, in someembodiments, the torque transfer assembly 185 may initially be installedwithin receptacle 146. Thereafter, in this example, lower end 120 b isinserted within receptacle 146 and engaged with assembly 185 in themanner previously described, thereby resulting in the arrangement shownin FIG. 15.

In the manner described, through direct engagement of such matingsurfaces (e.g., mating surfaces on keys 190, adapter 200, driveshaft120, and receptacle 146), driveshaft assembly 100 enables the transferof torque through direct, face-to-face surface contact as opposed topoint or line contact. Moreover, for driveshaft assembly 100,face-to-face surface contact is maintained between mating surfaces(e.g., mating surfaces on driveshaft 120, torque transfer assembly 185,and end housing 140), even as the driveshaft pivots about orthogonalpivot axes (e.g., pivot axes 127, 129). Torque transfer through suchdirect, face-to-face contact of surfaces offers the potential to greatlyreduce the rate of wear between the interacting surface and therebyincrease the running life of the driveshaft assembly (e.g., assembly100) and other related components.

While driveshaft assembly 100 has been described herein to include adriveshaft 120 with structurally identical ends 120 a, 120 b as well asstructurally identical socket sections 134, 144, it should beappreciated that other embodiments may not include such structuralsymmetry. Further, while pockets 302 within receptacle 146 have beendescribed as being defined by surfaces 310, 312, 314, 316, it should beappreciated that the exact size, shape, number, and arrangement ofpockets 302 within receptacle 146 may be greatly varied. Thus,embodiments of pockets 302 may assume any suitable shape that presentsone or more engagement surfaces for engagement with mating surfaces ontorque transfer assembly 185. Moreover, the specific shape andarrangement shown for pockets 302 in the Figures is merely illustrativeof one potential option for the design of pockets 302, and there is nointent to limit other potential embodiments of pockets 302 to thespecific shape shown therein. Similarly, it should also be appreciatedthat the specific number, shape, arrangement, and surfaces definingrecesses 124 on driveshaft 120 may be greatly varied in the same manner,and may assume any suitable shape, arrangement, number, etc., thatpresents one or more engagement surfaces for engagement with matingsurfaces on torque transfer assembly 185. Still further, whileembodiments of driveshaft 120 disclosed herein have included a sphericalthrust ball 122, it should be appreciated that in other embodiments,driveshaft 120 may not include cavity 121 and/or thrust ball 122. Forexample, in some embodiments, driveshaft 120 includes a convex sphericalbearing surface on end 120 a and/or end 120 b in place of thrust ball122 and/or cavity 121

Referring now to FIG. 16, another embodiment of driveshaft assembly 400is shown. Driveshaft assembly 400 is substantially the same asdriveshaft assembly 100 previously described, and thus, like numeralsare used to indicate like components and the description below willgenerally focus on the differences between assemblies 100, 400.Specifically, driveshaft assembly 400 includes the outer driveshafthousing 110, a driveshaft 420 rotatably disposed within housing 110, afirst or upper end housing 430 coupled to driveshaft 420, and a secondor lower end housing 440 also coupled to driveshaft 420.

Referring still to FIG. 16, driveshaft 420 has a central or longitudinalaxis 425, a first or upper end 420 a, a second or lower end 420 bopposite end 420 a, and a generally cylindrical radially outer surface420 c extending axially between ends 420 a, 420 b. As will be describedin more detail below, axis 425 of shaft 420 is not coaxially alignedwith axis 115 of housing 110.

Upper end housing 430 has a first or upper end 430 a, a second or lowerend 430 b opposite end 430 a, a connector section 432 extending fromupper end 430 a, and a socket section 434 extending from connectorsection 432 to lower end 430 b. In this embodiment, connector section432 is a male pin or ping end connector that threadably connects upperend housing 430 to the output shaft of hydraulic drive section 40 (seeFIG. 1). Socket section 434 receives upper end 420 a of drive shaft 420.As will be described in more detail below, the coupling between upperend 420 a and socket section 434 allows driveshaft 420 to pivot aboutend 420 a relative to end housing 430 while simultaneously transferringrotational torque and axial thrust loads between end housing 430 anddriveshaft 420.

Lower end housing 440 has a first or upper end 440 a, a second or lowerend 440 b, a connector section 442 extending from upper end 440 a, and asocket section 444 extending from connector section 442 to the lower end440 b. In this embodiment, connector section 442 is a female box orbox-end connector that threadably connects lower end housing 440 to themandrel of bearing assembly 80 (see FIG. 1). Socket section 444 receiveslower end 420 b of driveshaft 420. As will be described in more detailbelow, the coupling between lower end 420 b and socket section 444allows driveshaft 420 to pivot about end 420 b relative to end housing440 while simultaneously transferring rotational torque and axial thrustloads between end housing 440 and driveshaft 420.

In this embodiment, ends 420 a, 420 b of driveshaft 420 are structurallyidentical, and socket sections 434, 444 are structurally identical.Therefore, in the description to follow and associated Figures, thedetails of lower end 420 b, corresponding socket section 444, and theconnection therebetween are shown and described, it being understoodthat upper end 420 a, corresponding socket section 434, and theconnection therebetween, respectively, are the same.

Referring now to FIG. 17, lower end 420 b of driveshaft 420 and socketsection 444 of lower end housing 440 are shown. Socket section 444 has acentral or longitudinal axis 445 and includes a receptacle 446 thatextends axially from end 440 a and receives lower end 420 b ofdriveshaft 420. While axis 425 of driveshaft 420 and axis 445 are showngenerally aligned in FIG. 17, it should be noted that the axis 425 ofdriveshaft 420 is typically misaligned with axis 445 of socket section444 due to the pivoting of driveshaft 420 about end 420 b duringoperations.

Referring briefly to FIGS. 17, 23, and 24, receptacle 446 is defined bya radially inner surface 446 c. Moving axially from upper end 440 a,inner surface 446 c includes an upper generally cylindrical surface 608extending axially from upper end 440 a, a plurality of circumferentiallyspaced shoulders 606 extending radially inward from surface 608 (e.g.,in this embodiment, there are a total of four shoulders 606), aplurality of circumferentially spaced pockets 602 extending axially fromshoulders 606, a generally planar surface 604 extending radially frompockets 602, and a cylindrical counterbore or recess 620 extendingaxially from surface 604. Shoulders 606 and surfaces 604 are planarsurfaces disposed in planes oriented perpendicular to axis 445. Inaddition, in this embodiment, receptacle 446 includes a total of fourpockets 602 spaced uniformly circumferentially about axis 445, such thateach pocket 602 is disposed approximately 90° from eachcircumferentially adjacent pocket 602.

Referring back now to FIG. 17, in this embodiment, bearing insert 180,being the same as previously described above, is disposed within recess620. Insert 180 interacts with recess 620 in substantially the samemanner as described above for insert 180 and recess 320 (see FIG. 3),and thus, a detailed description of the structure of insert 180 and itsinteraction with recess 620 is omitted in the interests of brevity. Inaddition, as is also shown in FIG. 17, like lower end 120 b, previouslydescribed, lower end 420 b of shaft 420 includes cavity 121 thatreceives the thrust ball 122 in the same manner as previously describedabove. As a result, when lower end 420 b is mounted within receptacle446, upper end 181 a of body 181 extends into cavity 121 such thatconcave spherical bearing surface 182 mates with and slidingly engagesball 122. Further, as shown in FIG. 17, mounting collar 148, closureboot 164, rings 160, 163, 166 are couple to lower end 420 b and/orsocket section 444 in substantially the same manner as described abovefor lower end 120 b and socket section 144, respectively. Therefore, adetailed description of these components is also omitted in the interestof brevity.

Referring now to FIGS. 17-19, lower end 420 b of driveshaft 420 isshown. In addition to cavity 121 previously described, lower end 420 bincludes a plurality of recesses 424 extending radially inward fromouter surface 420 c and extending axially from lower end 420 b. Eachrecess 424 is at least partially defined by a convex cylindrical surface426, and a second planar surface 428. As will be described in moredetail below, during drilling operations, torque is transferred fromdriveshaft 420 through the surface 426 of each recess 424, and thus,convex cylindrical surface 426 of each recess 424 may be referred toherein as either an engagement or torque transfer surface 426. Inaddition, lower end 420 b of driveshaft 420 includes a first pivot axis427 and a second pivot axis 429. Axes 427, 429 are referred to herein as“pivot” axes because, as described in more detail below, shaft 420 isfree to pivot at lower end 420 b about one or both of axes 427, 429during rotation thereof about central axis 425. Axes 427, 429 areoriented orthogonal to each other and intersect at a center point 419disposed along axis 425. Thus, axes 425, 427, 429 all intersect atcenter 419. In addition, axes 427, 429 lie in a plane orientedperpendicular or orthogonal to axis 425. Further, in this embodimentcenter 419 also corresponds to the center of curvature of concavespherical surface 123 in cavity 121 and the center of thrust ball 122when ball 122 is installed within cavity 121 as previously described(e.g., see FIG. 17). Thus, sliding engagement between thrust ball 122and surface 123 of cavity 121 and sliding engagement between ball 122and surface 182 of bearing insert 180 allows driveshaft 420 to pivotabout center 419 during operations.

In this embodiment, lower end 420 b includes a total of four recesses424 circumferentially spaced uniformly about axis 425, such that eachrecess 424 is disposed approximately 90° from each circumferentiallyadjacent recess 424. As a result, for each recess 424, the surface 426is concentrically disposed about one of the pivot axes 427, 429 and thesurface 428 is perpendicular to one of the pivot axes 427, 429. Thus,each recess 424 is substantially V-shaped when viewed in cross-sectionalong axis 425 (e.g., as shown in FIG. 19). In addition, surfaces 426 ofeach pair of radially opposed recesses 424 with respect to axis 425(i.e., recesses that are disposed 180° from one another about axis 425)are each concentrically disposed about the same axis 427 or 429.Moreover, in this embodiment, each of the surfaces 428 are parallel tothe central axis 425 of driveshaft 420; however in other embodiments,surfaces 428 are not parallel to axis 425 and are instead disposed atsome non-zero angle thereto.

Referring now to FIGS. 17 and 20, a plurality of torque transfer keys490 is disposed about lower end 420 b of driveshaft 420 withinreceptacle 446 to transmit torque loads between driveshaft 420 and endhousing 440 as driveshaft 420 rotates about axis 425. As will bedescribed in more detail below, sliding engagement of correspondingmating surfaces of torque transfer keys 490, lower end 420 b, andreceptacle 446 allow driveshaft 420 to transfer torque to end housing440 through direct, face-to-face engagement even as driveshaft 420pivots about axes 427, 429 relative to end housing 440 as previouslydescribed.

Referring now to FIGS. 21-23, each of the torque transfer keys 490 isgenerally C-shaped and comprises a body 492 having a central axis 495, afirst or top side 492 a, a second or bottom side 492 b axially oppositethe top side 492 a, a first lateral side 492 c, and a second lateralside 492 d radially opposite the first lateral side 492 c. In thisembodiment, the axis 495 passes through the center of mass of key 490and is parallel to one of the axes 427, 429 when driveshaft assembly 400is fully made up. In addition, in this embodiment, side 492 a comprisesa planar surface 493 that is oriented perpendicular to axis 495 and side492 b comprises a convex or outwardly curved surface 499. In addition,in this embodiment, side 492 c comprises a planar torque transfersurface 494 extending axially between sides 492 a, 492 b, and side 492 dcomprises a concave cylindrical torque transfer surface 496 extendingaxially between sides 492 a, 492 b. A pair of parallel planar surfaces491, 498 extend between each of the planar surface 494 and the concavecylindrical surface 496 and also extend axially between planar sides 492a, 492 b. Surface 496 is concentric about an axis of curvature 497 thatis oriented parallel to axis 495 and surface 494, and radially spacedfrom axis 495 and surface 494. Axes 495, 497 lie in a plane orientedperpendicular to surface 494. Further, as will be described in moredetail below, in this embodiment, axis 497 of each key 490 is alignedwith one of the pivot axes 427, 429 when key 490 is installed on lowerend 420 b of driveshaft 420. Still further, in this embodiment, thetransitions between the surfaces 493, 499 and each of the surfaces 491,494, 496, 498 are chamfered in order to allow for proper clearances whenassembly 400 is fully made up. Also, in this embodiment, planar surface498 is larger than planar surface 491 such that keys 490 willsubstantially conform to the shape of recess 424 during operations;however, it should be appreciated that such an arrangement is notrequired and in other embodiments surface 491, 498 may be the same sizeor surface 491 may be larger than surface 498.

Referring again to FIGS. 24 and 25, in this embodiment each pocket 602of receptacle 446 is defined by a first planar surface 610, a secondplanar surface 612 parallel to the first planar surface 610, a thirdplanar surface 614 extending perpendicularly relative to both thesurfaces 610, 612, a fourth planar surface 616 extending betweensurfaces 612, 614, and a fifth planar surface 617 extending betweensurface 610, 614. The transitions between each of the surfaces 610, 612,614, 616 are radiused in order to increase the manufacturing efficiencyof housing 440 as well as to ensure proper clearance of interlockingcomponents during operations. Moreover, in this embodiment, each of thesurfaces 610, 612, 614, 616 extend axially or parallel to axis 445 ofend housing 440. As will be described in more detail below, each of thefirst planar surfaces 610 of pockets 602 engage with mating surfaces ontorque transfer keys 490 in order to transfer torque between shaft 420and end housing 440 during rotation of driveshaft 420 about axis 425.Thus, surfaces 610 may be referred to herein as either engagement ortorque transfer surfaces 310.

As is also best shown in FIG. 25, pockets 602 are arranged withinreceptacle 446 such that the first planar engagement surface 610 of eachpocket 602 extends to the second planar surface 612 of the immediatelycircumferentially adjacent pocket 602. In addition, the first planarengagement surfaces 610 of radially opposing pockets 602 (i.e., pockets602 that are circumferentially disposed 180° from one another about axis445) are generally parallel to one another. Such a parallel relationshipof surfaces 610 ensures that torque transfer between driveshaft 420 andend housing 440 is more evenly distributed.

Referring now to FIGS. 18, 20, and 21-23, during make up of driveshaftassembly 400, each of the keys 490 is disposed within one of therecesses 424 on lower end 420 b. In particular, each key 490 is disposedwithin one of the recesses 424 such that planar surface 493 slidinglyengages planar surface 428, and concave cylindrical surface 496slidingly engages convex cylindrical surface 426. In addition, as isbest shown in FIG. 20, when keys 490 are disposed within recesses 424 asdescribed above, the axis of curvature 497 of each surface 496 on eachkey 490 aligns with and is therefore coincident with one of the pivotaxes 427, 429 of driveshaft 420. Thus, during operations, each key 490is allowed to pivot or rotate about one of the pivot axes 427, 429through sliding engagement of the surfaces 426, 496 and slidingengagement of surface 493 and surface 428. This arrangement facilitatesthe pivoting of driveshaft 420 about axes 427, 429 relative to endhousing 440. In addition, in this embodiment, either prior or subsequentto installation of torque transfer keys 490 on lower end 420 b, thrustball 122 is installed within cavity 121 and is seated on concavespherical bearing surface 123 (e.g., see FIG. 17).

Referring now to FIGS. 17 and 26, lower end 420 b of driveshaft 420,with torque transfer keys 490 installed thereon in the manner describedabove, is then inserted within receptacle 446 on end housing 440 suchthat upper end 181 a of body 181 of bearing insert 180 extends intocavity 121 and concave spherical bearing surface 182 on upper end 181 aengages thrust ball 122. In this arrangement, thrust ball 122 isdisposed between and engaged with concave spherical bearing surfaces123, 182 as shown in FIG. 17. In addition, as lower end 420 b ofdriveshaft 420 and keys 490 are installed within receptacle 446,surfaces 494 on keys 490 slidingly engage with the correspondingengagement surfaces 610 of pockets 602 as shown in FIG. 26.

Referring still to FIGS. 17 and 26, once driveshaft assembly 400 isfully made up, driveshaft 420 is free to pivot relative to lower endhousing 440 about center 419, while rotating about axis 425. Inparticular, as shaft 420 rotates about axis 425 in direction 413, lowerend 420 b can pivot about one or both of the axes 427, 429 throughsliding engagement of thrust ball 122 on surface 123 within cavity 121and concave spherical bearing surface 182 of insert 180. Additionally,pivoting of end 420 b of driveshaft 420 about axes 427, 429 is furtheraccommodated by sliding engagement of cylindrical surface 496 of eachkey 490 and cylindrical surface 426 of each corresponding recess 424 onlower end 420 b of driveshaft 420, as well as sliding engagement ofplanar surface 493 of each key 490 and planar surface 428 of thecorresponding recess 424. It should be appreciated that in someembodiments, keys 490 move relative to pockets 602 during the rotationand pivoting of driveshaft 420 described above, and thus, the planarsurface 494 of each key 490 also sliding engages the planar engagementsurface 610 of each corresponding pocket 602 during these operations.

Moreover, during rotation of shaft 420 about axis 425 in direction 413,torque is transferred between lower end 420 b and end housing 440through torque transfer keys 490. In particular, torque is firsttransferred between lower end 420 b and keys 490 through engagement ofcylindrical surfaces 426, 496. Thereafter, torque is transferred betweenkeys 490 and end housing 440 through engagement of surfaces 494, 610.Because keys 490 are configured to pivot about one of the axes 427, 429relative to recesses 424 on lower end 420 b of driveshaft 420 in thepreviously described embodiment, keys 490 are able to maintainface-to-face contact between surfaces 496, 426 and surfaces 494, 610 asdriveshaft 420 pivots about axes 427, 429 simultaneous with rotationabout axis 425 in direction 413. In this embodiment, the couplingbetween upper end housing 430 and upper end 420 a of driveshaft 420 isstructurally and functionally the same as the coupling between lower endhousing 440 and lower end 420 b of driveshaft described above; however,it should be appreciated that such structural symmetry is not required.

In the manner described, through direct engagement of such matingsurfaces (e.g., mating surfaces on keys 490, driveshaft 420, andreceptacle 446), driveshaft assembly 400 enables the transfer of torquethrough direct, face-to-face surface contact as opposed to point or linecontact. Moreover, for driveshaft assembly 400, face-to-face surfacecontact is maintained between mating surfaces (e.g., mating surfaces ondriveshaft 420, torque transfer keys 490, and end housing 440), even asthe driveshaft pivots about orthogonal pivot axes (e.g., pivot axes 427,429). Torque transfer through such direct, face-to-face contact ofsurfaces offers the potential to greatly reduce the rate of wear betweenthe interacting surface and thereby increase the running life of thedriveshaft assembly 400 and other related components.

While driveshaft assembly 400 has been described herein to include adriveshaft 420 with structurally identical ends 420 a, 420 b as well asstructurally identical socket sections 434, 444, it should beappreciated that other embodiments may not include such structuralsymmetry. Further, while pockets 602 within receptacle 446 have beendescribed as being defined by surfaces 610, 612, 614, 616, it should beappreciated that the exact size, shape, number, and arrangement ofpockets 602 within receptacle 446 may be greatly varied. Thus,embodiments of pockets 602 may assume any suitable shape that presentsone or more engagement surfaces for engagement with mating surfaces ontorque transfer keys 490. Moreover, the specific shape and arrangementshown for pockets 602 in the Figures is merely illustrative of onepotential option for the design of pockets 602, and there is no intentto limit other potential embodiments of pockets 602 to the specificshape shown therein. Similarly, it should also be appreciated that thespecific number, shape, arrangement, and surfaces defining recesses 424on driveshaft 420 may be greatly varied in the same manner, and mayassume any suitable shape, arrangement, number, etc., that presents oneor more engagement surfaces for engagement with mating surfaces ontorque transfer keys 490. Still further, while embodiments of driveshaft420 disclosed herein have included a spherical thrust ball 122, itshould be appreciated that in other embodiments, driveshaft 420 may notinclude cavity and/or thrust ball 122. For example, in some embodiments,driveshaft 420 includes a convex spherical bearing surface on end 120 aand/or end 120 b in place of thrust ball 122 and/or cavity 121

While specific embodiments have been shown and described, modificationsthereof can be made by one skilled in the art without departing from thescope or teachings herein. The embodiments described herein areexemplary only and are not limiting. Many variations and modificationsof the systems, apparatus, and processes described herein are possibleand are within the scope of the disclosure. Accordingly, the scope ofprotection is not limited to the embodiments described herein, but isonly limited by the claims that follow, the scope of which shall includeall equivalents of the subject matter of the claims. Unless expresslystated otherwise, the steps in a method claim may be performed in anyorder. The recitation of identifiers such as (a), (b), (c) or (1), (2),(3) before steps in a method claim are not intended to and do notspecify a particular order to the steps, but rather are used to simplifysubsequent reference to such steps.

What is claimed is:
 1. A driveshaft assembly, comprising: a driveshaftincluding a longitudinal shaft axis, a first end, a second end axiallyopposite the first end, a radially outer surface extending axially fromthe first end to the second end, and a plurality ofcircumferentially-spaced recesses extending radially inward from theradially outer surface at the first end, wherein each recess is at leastpartially defined by a convex cylindrical surface and a planar surfaceoriented parallel to the longitudinal axis; and a plurality of torquetransfer keys, wherein one torque transfer key is configured to beseated in each of the plurality of recesses, wherein each torquetransfer key includes a first planar key surface configured to slidinglyengage the planar surface of the corresponding recess and a concavecylindrical surface configured to slidingly engage the convexcylindrical surface of the corresponding recess.
 2. The driveshaftassembly of claim 1, wherein each convex cylindrical surface isconcentrically disposed about a first pivot axis or a second pivot axis,wherein the first pivot axis, the second pivot axis, and thelongitudinal axis are orthogonal, and wherein each planar surface isoriented perpendicular to the first pivot axis or the second pivot axis.3. The driveshaft assembly of claim 2, wherein each torque transfer keyis configured to pivot about the first pivot axis or the second pivotaxis relative to the driveshaft.
 4. The driveshaft assembly of claim 2,wherein the convex cylindrical surface of each torque transfer key has acenter of curvature aligned with the first pivot axis or the secondpivot axis.
 5. The driveshaft assembly of claim 1, wherein each torquetransfer key includes a convex surface opposite the first planar keysurface.
 6. The driveshaft assembly of claim 1, wherein the plurality ofrecesses comprises four uniformly circumferentially-spaced recesses andthe plurality of torque transfer keys comprises four torque transferkeys.
 7. The drive shaft assembly of claim 1, further comprising: afirst end housing, wherein the plurality of torque transfer keys areconfigured to transfer torque between the driveshaft and first endhousing.
 8. The driveshaft assembly of claim 7, wherein the first endhousing includes a longitudinal housing axis and a receptacle extendingaxially from an end of the first end housing, wherein the receptacleincludes a plurality of circumferentially-spaced planar receptaclesurfaces; wherein each torque transfer key includes a second planar keysurface opposite the concave cylindrical surface, wherein the secondplanar key surface of each torque transfer key is configured toslidingly engage one of the planar receptacle surfaces.
 9. A driveshaftassembly, comprising: a driveshaft including a longitudinal shaft axis,a first end, a second end opposite the first end, and a radially outersurface, wherein the first end includes a plurality of recessesextending radially inward from the radially outer surface, the recesseseach comprising a convex engagement surface; a first end housingincluding a longitudinal housing axis, and an axially extendingreceptacle, wherein the receptacle includes a plurality of planarreceptacle surfaces; and a plurality of torque transfer keys configuredto transfer torque between the driveshaft and first end housing, each ofthe torque transfer keys including a planar key surface and a concavekey surface; wherein: the convex engagement surface of each recessengages the concave key surface of one of the torque transfer keys; andthe planar key surface of each torque transfer key engages one of theplanar receptacle surfaces; wherein the plurality of recesses comprises:a first recess; a second recess circumferentially spaced 90° from thefirst recess about the shaft axis; a third recess circumferentiallyspaced 90° from the second recess about the shaft axis; and a fourthrecess circumferentially spaced 90° from each of the third recess andthe first recess about the shaft axis.
 10. The driveshaft assembly ofclaim 9, wherein the planar receptacle surfaces extend parallel to thehousing axis.
 11. The driveshaft assembly of claim 10, wherein theconcave key surface of each torque transfer key is configured toslidably engage the convex engagement surface of the correspondingrecess to accommodate pivoting of the driveshaft about one or more pivotaxes extending perpendicular to the shaft axis.
 12. The driveshaftassembly of claim 9, wherein the driveshaft is configured to pivot abouta first pivot axis and a second pivot axis relative to the first endhousing; wherein the first pivot axis is orthogonal to the second pivotaxis; wherein the first pivot axis and the second pivot axis are eachorthogonal to the shaft axis; and wherein the first pivot axis and thesecond pivot axis each cross the shaft axis at a center point.
 13. Thedriveshaft assembly of claim 5, wherein plurality of torque transferkeys comprises: a first torque transfer key disposed within the firstrecess such that the concave key surface of the first torque transferkey engages with the convex engagement surface of the first recess; asecond torque transfer key disposed within the second recess such thatthe concave key surface of the second torque transfer key engages withthe convex engagement surface of the second recess; a third torquetransfer key disposed within the third recess such that the concave keysurface of the third torque transfer key engages with the convexengagement surface of the third recess; and a fourth torque transfer keydisposed within the fourth recess such that the concave key surface ofthe fourth torque transfer key engages with the convex engagementsurface of the fourth recess.
 14. The driveshaft assembly of claim 13,wherein the first pivot axis is aligned with: a center of curvature ofthe convex engagement surface of the first recess; a center of curvatureof the convex engagement surface of the third recess; a center ofcurvature of the concave key surface of the first torque transfer key;and a center of curvature of the concave key surface of the third torquetransfer key.
 15. The driveshaft assembly of claim 14, wherein thesecond pivot axis is aligned with: a center of curvature of the convexengagement surface of the second recess; a center of curvature of theconvex engagement surface of the fourth recess; a center of curvature ofthe concave key surface of the second torque transfer key; and a centerof curvature of the concave key surface of the fourth torque transferkey.